1. Field of the Invention
The present invention relates to an image forming apparatus and a count control method, particularly to an image forming apparatus provided with a function of printing a watermark and a count control method of the image forming apparatus.
2. Description of Related Art
Copying machines and MFPs (Multi Function Peripherals), each having a color printing function, are becoming common, and various documents are printed in offices with those machines. Particularly, in cases of printing a document including confidential information, it is required to prevent leakage of such confidential information, so that recent image forming apparatuses are provided with a function known as watermark printing (for example refer to Unexamined Japanese Patent Application Publication Nos. S53-142237, and S54-74125). In the watermark printing, specific characters or patterns are printed to be embedded into an original document so as not to be recognized by the naked eye. Such embedded inconspicuous characters or patterns are called a watermark.
Further, in the case of billing based on a number of printed sheets, the number of color printed sheets and the number of monochrome printed sheets are separately counted because the billing amount is different between color printing and monochrome printing. Therefore, in cases where a color image is included in an original document, the number of sheets is counted as color printing.
However, since the watermark is inconspicuously printed, in the case of printing by embedding the watermark into the original document, or in the case of copying the original document previously embedded with the watermark, various inconveniences arise depending on whether to count as color printing or as monochrome printing.
The present invention has been accomplished in view of the above problem, and its primary object is to provide an image forming apparatus and count control method which are capable of eliminating the inconveniences arising in the case of printing the watermark.